The 2007 UNAIDS report estimated that for each person treated with potent antiretroviral therapy, 4-6 new individuals became infected. Without a foreseeable cure for HIV, prevention measures must control the HIV epidemic and structural/barrier/behavioral methods simply have limited efficacy or applicability. There is a critical need, for coitally-independent dosing strategies which women can initiate and are imperceptible to their partners. It is increasingly clear that antiretroviral pharmacokinetics predict efficacy: using samples from the CAPRISA 004 study, our laboratory demonstrated that subjects who maintained the highest tenofovir concentrations in cervicovaginal fluid (and thus in genital tract tissues) were the least likely to become infected with HIV-1 and HSV2. Although topical formulations such as gels and vaginal rings are being investigated, oral antiretroviral drugs also hold significant promise for prevention. Currently, antiretroviral doses used in prevention studies are those that are FDA-approved for treatment of HIV infection. However, there are no data to confirm that exposures with these standard treatment doses will protect mucosal cells from HIV acquisition, or to inform alternative dosing strategies. We propose a highly significant plan to develop a model for oral antiretroviral prevention strategies. In healthy women volunteers, we will determine the ability of 3 doses of 4 antiretroviral drugs to concentrate in 3 at-risk mucosal surfaces. In explant tissue cultures, the concentration of these drugs, alone and in combination, required to protect tissues exposed to multiple infectious molecular clones will be identified. A new approach to normalizing tissue responses to cell numbers and composition will also be implemented. Once the in vivo tissue pharmacokinetic results and ex vivo target concentration results are known, a mathematical model will be developed to predict the antiretroviral doses/regimen maximally protective at all mucosal surfaces. Finally, a second proof-of-concept study is proposed to dose women with the final antiretroviral regimen and challenge tissue biopsies with HIV to determine risk of infection. PUBLIC HEALTH RELEVANCE: There is a critical need for HIV prevention strategies which women control and are imperceptible to their partners. We propose a highly significant plan to develop a model for oral antiretroviral (ARV) prevention strategies. We will determine how 4 selected ARVs concentrate in 3 mucosal surfaces at risk for HIV infection. In tissue culture, ARV concentrations that protect tissues from HIV infection under multiple conditions will be identified. We will combine the aforementioned data in a mathematical model that will identify the most protective drug regimen to investigate in further clinical studies.